In general, a compressor is a mechanical apparatus receiving power from a power generation apparatus such as an electric motor, a turbine or the like, and compressing the air, refrigerant or various operation gases to raise a pressure. The compressor has been widely used for electric home appliances such as refrigerators and air conditioners, and application thereof has been expanded to the whole industry.
The compressors are roughly classified into a reciprocating compressor, wherein a compression space to/from which an operation gas is sucked and discharged is defined between a piston and a cylinder, and the piston linearly reciprocates in the cylinder to compress refrigerant, a rotary compressor, wherein a compression space to/from which an operation gas is sucked and discharged is defined between an eccentrically-rotating roller and a cylinder, and the roller eccentrically rotates along an inside wall of the cylinder to compress refrigerant, and a scroll compressor, wherein a compression space to/from which an operation gas is sucked and discharged is defined between an orbiting scroll and a fixed scroll, and the orbiting scroll rotates along the fixed scroll to compress refrigerant.
Korean Laid-Open Patent Publication No. 10-1996-0023817 discloses a rotary compressor, wherein a cylinder and a motor are stacked in an axial direction, so that refrigerant is compressed in the cylinder compressing a defined capacity. If a constant speed type motor is used as the motor, since the motor has a uniform rotational speed, it can regulate a compression capacity per hour to be uniform. However, if an inverter type motor is used as the motor, since the motor has a variable rotational speed, it can vary a compression capacity per hour.
Korean Laid-Open Patent Publication No. 10-2005-0062995 discloses a rotary type twin compressor, wherein two cylinders and a motor are stacked in an axial direction, so that refrigerant is simultaneously compressed in the two cylinders compressing the same capacity. As compared with a general compressor, this compressor doubles a compression capacity.
Korean Laid-Open Patent Publication No. 10-2007-0009958 discloses a rotary type two-stage compressor, wherein two cylinders and a motor are stacked in an axial direction, and a special passage is provided to connect the two cylinders, so that refrigerant compressed in one cylinder is compressed in the other cylinder. As compared with a general compressor, this compressor doubles a compression degree.
The rotary compressor is used in a freezing cycle. When the rotary compressor operates, oil is circulated to cool/lubricate inside components thereof. Here, some of the liquid-phase oil is discharged from the rotary compressor with gas-phase refrigerant. However, if the oil is excessively discharged from the rotary compressor to the freezing cycle, the components inside the rotary compressor are abraded/overheated due to lack of the oil, which reduces operation reliability. Otherwise, since the oil flows along the freezing cycle and lays on a passage due to a fall of a temperature and pressure, the oil is difficult to recover. Therefore, the rotary compressor adopts various oil recovery structures to prevent the oil from being discharged through the freezing cycle with high pressure refrigerant.
Meanwhile, the rotary compressor includes a compression mechanism unit and a motor unit driving the same. Motors are classified into a distributed winding type and a concentrated winding type according to winding methods.
In the distributed winding type, respective phase windings are wound around a few slots in a distributed manner. As a plurality of coil groups lay on the slots, a coil end increases in an axial direction of the winding, so that a space factor of the winding inserted into the slot is not high. Accordingly, in the rotary compressor using the distributed winding motor, since relatively many empty spaces are formed in the motor due to a not-high winding space factor, although oil is pumped, it can be recovered through the distributed winding motor. Although the rotary compressor does not adopt a special oil recovery hole or oil recovery structure, there is no difficulty.
In the concentrated winding type, windings are wound around one slot in a concentrated manner. A concentrated winding slot has a smaller area and more poles than a distributed winding slot. A coil is directly wound around the pole in a direct winding type, or inserted into an inside diameter slot opening groove of a stator in an insert winding type. As compared with the distributed winding type, a coil end decreases in an axial direction of the winding and a winding space factor increases. Therefore, in the rotary compressor using the concentrated winding motor, since relatively few empty spaces for use in recovering oil are formed in the motor due to a high winding space factor, although the oil is pumped, it cannot be easily recovered through the concentrated winding motor. Preferably, the rotary compressor adopts an oil recovery hole or oil recovery structure to easily recover the oil.
FIG. 1 is a vertical-sectional view illustrating an overall structure of a rotary compressor which is one example of the prior art, and FIG. 2 is an exploded view illustrating an attachment structure of an oil separation member applied to FIG. 1.
Japanese Patent Application No. 94-317020 discloses a rotary compressor and an oil recovery structure. As illustrated in FIGS. 1 and 2, a motor unit 11 and a compression unit 12 are provided in a hermetic casing 10, the motor unit 11 is composed of a stator 13, a rotor 14 and a rotation shaft 15, and an oil separation member 50 is mounted at a top end center of the rotor 14. Accordingly, when power is supplied, the rotation shaft 15 rotates due to a mutual electromagnetic force of the stator 13 and the rotor 14, so that refrigerant is compressed in the compression unit 12, filled in the hermetic casing 10, and discharged to the outside. In addition, oil stored in a bottom surface of the hermetic casing 10 rises along the rotation shaft 15. The oil flows through a central portion of the rotor 14, runs against the oil separation member 50 rotating with the rotor 14, is guided to a radius direction, and is recovered to the bottom surface of the hermetic casing 10 through a plurality of holes 54 bored through the periphery of the central portion of the rotor 14 in an axial direction as well as a gap between the stator 13 and the rotor 14.
However, in the conventional rotary compressor, although the oil is pumped, since the oil runs against the oil separation member, it is recovered through the holes of the rotor which are limited spaces and the gap between the stator and the rotor. In the case of the inverter type compressor, although the oil is excessively pumped due to velocity variations, only some of the oil is recovered through the limited spaces, so that an oil recovery rate to the rotary compressor is reduced. Since the oil discharged from the rotary compressor flows through the freezing cycle adopting the rotary compressor and lays on piping, it is difficult to recover the oil to the rotary compressor. As a result, components in the rotary compressor may be abraded, which degrades operation reliability.
FIG. 3 is a graph analyzing oil flowing paths of a conventional rotary compressor. The rotary compressor shown in FIG. 3 is identical to the rotary compressor shown in FIG. 1 except that the oil separation member is omitted. When the rotary compressor operates to compress refrigerant, oil rises through a main passage portion A around a rotation shaft with the refrigerant, runs against a hermetic casing, and is recovered through a recovery passage portion B around the main passage portion A. Here, the recovery passage portion B is composed of first recovery passages B1 which are a plurality of holes bored through the periphery of a central portion of a rotor in an axial direction as described above, a second recovery passage B2 which is a gap between a stator and the rotor, and a third recovery passage B3 which is a space between the hermetic casing and the stator. The passages capable of recovering the oil are widened. Surely, although the oil vertically rising through the main passage portion A runs against the hermetic casing, a comparatively large amount of oil is recovered through the first and second recovery passages B1 and B2 relatively adjacent to the main passage portion A, but a comparatively small amount of oil is recovered through the third recovery passage B3 relatively distant from the main passage portion A.
In the rotary compressor, since the recovery passage portion is smaller than the main passage portion, the oil recovery rate decreases. While the velocity of the oil pumped through the main passage portion is fast (about 10 m/s), the velocity of the oil recovered through the recovery passage of the recovery passage portion positioned at the outermost portion is slow (about 0.005 m/s). Therefore, a large amount of oil stays in an upper portion of the hermetic casing, and is easily discharged to the outside of the hermetic casing with high temperature high pressure refrigerant. Moreover, since the oil recovery rate decreases, as mentioned above, operation reliability is degraded due to friction/abrasion of components.